package seguridad;

/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.io.*;
import java.security.*;
import java.security.spec.*;

class Verificar
{

    public static void main( String[] args )
    {

        /* Verify a DSA signature */

        if( args.length != 3 )
        {
            System.out.println( "Usage: VerSig publickeyfile signaturefile datafile" );
        }
        else
            try
            {

                /* import encoded public key */

                FileInputStream keyfis = new FileInputStream( args[ 0 ] );
                byte[] encKey = new byte[keyfis.available( )];
                keyfis.read( encKey );

                keyfis.close( );

                X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec( encKey );

                KeyFactory keyFactory = KeyFactory.getInstance( "DSA", "SUN" );
                PublicKey pubKey = keyFactory.generatePublic( pubKeySpec );

                /* input the signature bytes */
                FileInputStream sigfis = new FileInputStream( args[ 1 ] );
                byte[] sigToVerify = new byte[sigfis.available( )];
                sigfis.read( sigToVerify );

                sigfis.close( );

                /* create a Signature object and initialize it with the public key */
                Signature sig = Signature.getInstance( "SHA1withDSA", "SUN" );
                sig.initVerify( pubKey );

                /* Update and verify the data */

                FileInputStream datafis = new FileInputStream( args[ 2 ] );
                BufferedInputStream bufin = new BufferedInputStream( datafis );

                byte[] buffer = new byte[1024];
                int len;
                while( bufin.available( ) != 0 )
                {
                    len = bufin.read( buffer );
                    sig.update( buffer, 0, len );
                }
                ;

                bufin.close( );

                boolean verifies = sig.verify( sigToVerify );

                System.out.println( "signature verifies: " + verifies );

            }
            catch( Exception e )
            {
                System.err.println( "Caught exception " + e.toString( ) );
            }
        ;

    }

}
